A screw kneader of this type is disclosed in DE-OS 15 54 761, wherein a cylindrical or spherical transfer segment is arranged between the threads in the mixing section and the threads in the inlet and outlet sections. The transfer segment has the disadvantage of producing build-up or accumulation of plastic material in the mixing section. The transfer of plastic material to and from the mixing section becomes discontinuous and consequently the residence time of the mixed material is non-uniform. The self-cleaning effect of the threads in the mixing section and the inlet and outlet sections is negated in the transfer segments and deposits of plastic material are formed which lead to a reduction in the quality of the mixed material. Mixing of additives with the basic plastic material is not provided.
Another multipurpose mixing and kneading apparatus, also operating continuously, is disclosed in DE OS 16 57 574 wherein the transfer segments have formed transfer surfaces arranged in a staggered manner with respect to the threads of the kneader so that a self-cleaning effect is also obtained in the transfer regions. This self-cleaning effect, however, has no effect on the walls of the bores in the housing, so that at least in this region so-called dead zones are formed. The transfer surfaces cooperate symmetrically in pairs and serve exclusively for the formation of kneading surfaces and thus for dispersive treatment of the mixed material by the introduction of shearing energy. Since flows of mixed material are not formed, any dispersion and distribution of the mixed material does not occur within the kneading apparatus. Hence, this apparatus is not suitable for the intermixing and homogeneous distribution of additive components.